An OTDR is an instrument used to detect and characterize features in an optical fiber. These features may include spontaneous increase of signal level due to reflection at a small air gap between parts of a connector, or a drop of signal level caused by a splice loss or a power splitter. In some situations, reflectance or optical loss could represent a defective fiber.
An OTDR analyzes optical signals through an optical fiber and may output such signals as OTDR traces. OTDR traces are generally captured in the presence of noise making it difficult to detect or reliably characterize signal characteristics having a magnitude less than that of the noise.
In addition to noise, dynamic range and dead-zone of OTDR traces are relevant to OTDR instrumentation. Dynamic range is a backscatter level at the entrance of a fiber compared to noise level such that a better dynamic range indicates a smaller noise level. Dead-zone is a section of an OTDR trace immediately following a spontaneous increase of signal level due to reflection, such that a trace may appear functionally saturated, before the power of received light falls within some level, such as 1.5 dB for reflective event and 0.5 dB for non-reflective event.
Present techniques for overcoming such noise and inability to interpret signal characteristics, such as within a dead-zone of an OTDR trace, have disadvantageous. Increasing the power of a light pulse may increase the complexity and price of an instrument, as well as may cause safety issues. Averaging repeated measurement results may increase test time and thereby decrease productivity. Increasing a duration of a light pulse may cause an OTDR trace to exhibit at least longer dead-zones thereby preventing any measurement during a greater portion of the trace. Applying a filter to an OTDR trace may have similar effect as increasing a duration of a light pulse, and the effect of the filter may diminish as length of the filter increases. Accordingly, a technique for OTDR traces is needed which may overcome these disadvantages.